Five defense witnesses took the stand yesterday in the murder trial of Bernard C. Welch, but their testimony failed to provide an alibi for the whereabouts of Welch on the night of Dec. 5, when physician Michael Halberstam was slain.

In an attempt to refute allegations that Welch burglarized homes in Halberstam's neighborhood and later fatally shot the doctor, the witnesses -- Welch's housekeeper, two contractors employed at his Great Falls home and his common-law wife -- each assured a D.C. Superior Court jury that Welch had been in their sight almost the entire day, supervising their work and talking on the telephone. But not one could explain his whereabouts in the vital evening hours when prosecutors contend he fatally shot Halberstam.

And, in an effort to prove that Welch had not been out casing Halberstam's neighborhood that afternoon and indeed was a respectable buyer of precious metals, Welch's wife, Linda Sue Hamilton, made the potentially damaging disclosure that Welch had gone out that day to purchase propane gas for use in melting goal and silver.

She proceeded to describe in detail how Welch would melt bracelets, earrings and other metal objects, then mail gold bars to a Calfornia refinery. She even produced a receipt for the propane gas purchase, saying that she and Welch had "saved it for tax purposes," apparently intending to deduct it as a business expense.

As she spoke, thousands of dollars worth of jewelry a table in front of the jury, and government prosecutors, who previously had not mentioned Welch's elaborate smelting operations, prodded her further.

Welch himself declined to testify, apparently to keep the nine-woman, three-man jury from learning of his lengthy criminal record. But the essence of his defense is this: There are no eyewitnesses to the Halberstam slaying, and government witnesses who place him at the scene are mistaken.

In a surprisingly short defense lasting less than two hours, Welch's attorney, Sol. Z. Rosen, told the jury that "the government has picked the wrong man."

The U.S. attorney's office rested its case earlier in the day after a D.C. police ballistics expert and an FBI analyst testifed that Halberstam was fatally shot at point-blank range with bullets from a gun traced to Welch. Two of the bullets pierced Halberstam's lung and killed him, a medical examiner testified.

For the first time during the week-long trial, Welch seemed nervous and drawn, biting his nails, twirling a pen in his mouth, rubbing his face with his hand. Rosen, however, told reporters later that Welch is in a "pretty jovial mood, and wants to finish the trial.

"We've got a fifty-fifty chance [of winning]," Rosen said. "We've broken some holes in the government's case. All I have to do is leave a reasonable doubt in some of the jurors' minds."

Rosen's defense of Welch concentrated on two identifications made of Welch -- one by Halberstam's widow, Elliott Jones, who testified she saw her dying husband ram his car into a man police say is Welch; and a neighbor's maid, Mamie Stallworth, who testifed that she saw Welch drive past Halberstam's house twice on the afternoon of Dec. 5. The government contends he was casing the house for a burglary attempt.

Rosen elicited testimony from a D.C. police detective that Stallworth saw a television photograph of Welch before she picked him out of a police lineup.

Rosen complained to reporters that Stallworth's identification at the lineup was tantamount to "shooting ducks in a barrel."

The defense lawyer also has contended that Jones' identification of Welch after the shooting was suggestive because police pointed him out to her while he was lying in an ambulance. The identification took place shortly after the dying Halberstam rammed his car into Welch, telling his wife, "That's the guy!"

While none of Welch's witnesses could testify as to his whereabouts when Halberstam was shot, the defense testimony -- especially Hamilton's -- for the first time described for the jury the personal life of the man who had sat in the courtroom in a blue suit, never spoken a word to the jurors, and repeatedly been called by three names: Welch, and aliases Norman Hamilton and Norm Heiman.

Hamilton, who is the mother of Welch's three infant children, testified that together they bought and sold silver and gold, which they smelted in a furnace in their garage. The smaller pieces of jewelry -- such as earrings and wedding bands -- were smelted immediately, which larger pieces first "had to be broken down."

She did not disclose where the jewelry was obtained, but said Welch mailed the finished bars to a California refinery. She said Welch purchased propane gas from a Virginia firm called Beltway Oxygen for tanks located in their garage.

It was Beltway Oxygen, Hamilton testified, where Welch went last Dec. 5, but she admitted under questioning from Assistant U.S. Attorney Jay B. Stephens that when she returned to her home at 10 p.m. that night, Welch was not there.

Hamilton, who previously testified for the prosecution, already had told the jury that neither Welch nor the couple's silver Mercedes was at home when she awoke the next morning.

Prosecutors yesterday tried to discredit Hamilton's testimony on Welch's behalf by attempting to show that she had an interest in the outcome of the case. "You've been living with Bernard Welch for five years," Stephens stated at one point. "You've had three children by him."

"Yes."

"You don't want to see him go to jail, do you?"

"No."

"You don't want to believe he's a thief?"

Again, No."

. . . a murderer?"

"No."

Under questioning from Assistant U.S. Attorney Alexia Morrison, defense witness Marvin Goode, Welch's electrical contractor, recalled that on Dec. 5 Welch was wearing blue jeans and a blue ski jacket at his Great Falls home. When Welch was arrested later that night he was wearing blue jeans and a blue ski jacket.

The prosecution rested its case after Deputy D.C. Medical Examiner Brian Blackbourne testified Halberstam was hit twice by gunfire from a distance of three inches.

The case goes to the jury today.